[attachment=10959]
FOUR-QUADRANT CHOPPER DRIVE FOR DC MOTOR
Objective:
The aim of the project is to develop a speed control system for DC motor using four-quadrant chopper. Using four-quadrant chopper it is possible to demonstrate forward &reverse motoring and braking.
Theory:
The speed of DC motor is directly proportional to armature voltage and inversely proportional to flux. By maintaining the flux constant, the speed can be varied by varying the armature voltage. The direction of rotation is reversed by reversing either field or armature voltage.
Functioning:
In this project, motor field is excited by the fixed dc voltage obtained from uncontrolled rectifier. The armature is excited by a variable dc supply obtained from four-quadrant chopper.
The system is provided with various control keys, such as START, STOP, FORWARD, REVERSE, FORWARD BRAKE, and REVERSE BRAKE. Using these keys, the user can set the motor to run in any one of the following modes, namely Forward motoring, Reverse motoring, Forward braking and Reverse braking. The speed can be varied by varying the voltage given to the PWM converter (using potentiometer).
Moreover, the system is provided with Soft start facility i.e., starting the motor without allowing the armature current to exceed the full load current.
Hardware:
The Hardware of this system includes uncontrolled rectifier using diodes, chopper using either MOSFETs or IGBTs, control keys, speed adjust potentiometer and other logical circuits.